Page History
...
4A. Select forecast day or period from drop-down menu. 4B. Select quantile. 4C. Select Area from drop-down menu.
Fig8197.AFig8.1.9.7-1: To view Medium Range CDFs:
...
- Quantile1: 1 in 100 occasions in the M-climate was lower than the value shown.
- Quantile10: 1 in 10 occasions in the M-climate was lower than the value shown.
- Quantile50: 1 in 2 occasions in the M-climate was lower than the value shown (i.e. the median)
- Quantile90: 1 in 10 occasions in the M-climate was greater than the value shown.
- Quantile99: 1 in 100 occasions in the M-climate was greater than the value shown.
Fig8197.BFig8.1.9.7-2: Example of EFI and SOT chart for mean temperature for the period T+48 to T+72 (VT 00UTC 30 Mar 2018 to VT 00UTC 31 Mar 2018), DT 00UTC 28 Mar 2018.
On Fig8197.B Fig8.1.9.7-2 (left chart):
- Blue colours over Portugal indicate EFI between 0.8 and 0.9 for a colder than normal event. Positive SOT is indicated within the black zero SOT contour.
- Orange and red colours over parts of Italy and Sicily indicate EFI between 0.8 and 1.0 for a warmer than normal event. A small positive SOT is indicated within the black zero SOT contour.
EFI values above/below ±0.8 usually signify a very unusual or extreme event. Positive SOT values indicate that at least 10% of the ensemble is forecasting an extreme event. A high value of SOT shows how extreme the lower or higher 10% ensemble results are. For more information see the sections on Extreme Forecast Index (EFI) and Shift of Tails (SOT).
On Fig8197.B Fig8.1.9.7-2 (right chart):
Colours indicate the quintile90 temperature ranges of the M-climate where only one in 10 occasions have reached greater values than shown (i.e. on only 1 in 10 occasions during the construction of M-climate for each location and on this date have the temperatures indicated by the colours been exceeded). The chart shows on only 1 in 10 occasions are mean temperatures likely to be above 15°C-20°C in parts of southern Italy and Sicily. The high EFI and locally positive SOT in these areas suggests unusually high mean temperatures may be expected. Selection of quintile10 would allow a similar assessment of how unusually cold the mean temperature in Portugal is likely to be.
...
Multi-parameter interactive charts are available showing the geographical distribution of the EFI of the principal weather parameters: maximum 10m wind gust, 24hr precipitation and 2m temperature, overlaid with the ensemble mean of the MSLP field. This chart highlights areas where there is a significant difference between the ensemble forecast (ensemble) distribution and the model climate (M-climate) distribution.
...
- 10 day meteogram
- 15 day meteogram
- 15 day meteogram with M-climate
- plume
- 10 day wavegram
- EFI-CDF
- Vertical profile
...
- A range of CDFs are available:
- 24hour mean 2m temperature.
- 24hour minimum 2m temperature.
- 24 hour maximum 2m temperature.
- 24 hour maximum wind gust.
- 24 hour precipitation.
- A range of EFIs are available:
- 2m temperature.
- 24 hour maximum wind gust.
- 24 hour total precipitation.
Fig8197.EFig8.1.9.7-5: Examples of EFIs and CDFs from a series of ensemble runs for Valetta VT 30 Mar 2018. The location can be chosen by the user by the probe tool on ecCharts or by use of widgets on the dashboard.
...
Attached to each grid point of the global EFI charts there is a CDF diagram for each of the EFI parameters, with information on M-climate at the grid point (always shown for the lead time 24-48h) and the available forecast distributions (all valid for the given day, but coming from different, consecutive ensemble runs, so the lead times vary). On the right are shown the corresponding EFI values. These diagrams can be displayed interactively by clicking on the desired location on the EFI web charts, use of the probe tool on ecCharts, or selection of the widgets on the dashboard.
Fig8197.FFig8.1.9.7-6: CDF and associated EFI for NW Portugal area. There is a consistently high and increasing EFI for rainfall (reaching 80%) which is sufficient for forecasting a significant and maybe an extreme rainfall event. Some ensemble members show rainfall totals much greater than M-climate maxima - the degree to which these totals exceed the M-climate maximum is not taken account of in the EFI calculation, but is used directly in calculating SOT. The EFI for maximum wind gust is greater than 50% in the last two forecasts but this is not really sufficient for forecasting a significant wind event. The steep and consistent temperature CDF indicates high confidence in a forecast of near normal temperatures around 14°C.
Fig8197.GFig8.1.9.7-7: CDF and associated EFI for Po Valley area. EFIs for mean temperature and wind gusts are consistently negative but not large. The CDF shows consistency between the temperature forecasts, with the last ensemble forecast a little colder. The steep CDF indicates high confidence in a forecast of about 2°C below normal temperature.
Fig8197.HFig8.1.9.7-8: CDF and associated EFI for Marseilles area. There is a consistently high and increasing EFI for wind (reaching 86%) which is sufficient for forecasting a significant and possibly extreme wind event. The CDF shows consistency between the stronger gust forecasts in last two ensemble results. Some ensemble members show wind gusts much greater than M-climate maxima - the degree to which these values exceed the M-climate maximum is not taken account of in the EFI calculation, but is used in calculating SOT. The steep and consistent mean temperature CDF indicates high confidence in a forecast of near normal temperatures around 16°C.
Fig8197.IFig8.1.9.7-9: CDF and associated EFI for NE Poland area. There is a strong and consistent negative EFI for temperature. The CDF traces are steep and very similar over last four forecast runs and imply high confidence in out of the ordinary cold mean temperatures about 8°C below normal.
...
The example given in Fig8.1.49.7.7 -10 was associated with a frontal wave system that, although not appearing very dramatic on the synoptic charts, produced significant rainfall as it moved briskly northeastward across parts of northern USA and eastern Canada.
Fig8197.JFig8.1.9.7-10: An example of the use of EFI and SOT during the period leading up to 05-06 September 2018. The evolution of this sequence illustrates the ability of EFI and SOT charts to allow early indication the risk of severe weather (SOT), with an indication of changes in confidence and definition of the area at risk (EFI). EFI tends to be greater than 0.5 if the majority of ensemble member forecast values are markedly greater than those of the corresponding M-climate. EFI>0.5 is coloured (see scales). SOT>0 if at least 10% of ensemble members forecast an extreme event. Isopleths are for values of 0,1,2,5,8. The actual SOT values show how extreme the top 10% of ensemble forecast are.
Chart A (from a forecast 6 days ahead of the event) shows fragmented areas where SOT>0 (i.e. a few ensemble members show an extreme event) so a very severe weather event is possible. However, generally low EFI values (<0.5) shows the majority of ensemble members do not indicate an unusual event (even though a few do).
...
Chart D (from a forecast 0 days ahead of the event) shows the areas of SOT>0 and EFI>0.5 are tightly defined, giving confidence to the user in pinpointing the areas at risk. There is an elongated internal area where SOT>1.0, even SOT >2.0, so a very severe event is possible. EFI values are more widely >0.8 (dark orange) so confidence of at least a severe event is growing (for those areas)
Fig8197.KFig8.1.9.7-11: Observed rainfall totals include some above 50mm/24hr and one above 100mm/24hr over eastern Canada during the period 05/12UTC to 06/12UTC September 2018.
...
The ensemble is designed to give an assessment of uncertainty. However, occasionally the uncertainty becomes very large, with additionally a potential for very high or low forecast values to occur. An example is shown in Fig8.1.49.7.9 -12 where ensemble members showed widely differing yet potentially extreme hot or cold temperatures. These cases are relatively rare, usually associated with a sharp upper trough and associated front separating widely dissimilar airmasses. Users should accept the uncertainty and tailor their forecasts to reflect the impact on users. Certainly they should not take middle course. Some customers may require an indication of very high or very low temperatures, even if at a low probability.
Fig8197.LFig8.1.9.7-12: EFI and SOT chart VT 22-23 July 2012 (T+156-180) from ensemble DT 00UTC 15 July 2012, with associated Cumulative Distribution Function (CDF) and meteogram with M-climate for the marked position. The uncertainty is clear on the meteograms. The CDF shows some ensemble members indicating temperature values above M-climate maximum and some below M-climate minimum and thus the SOT will show values for both the warm and cold tails. This is shown on the chart where the SOT lines (black) overlap. The airmasses are clearly very different as there is a large positive EFI indicative of high temperatures over eastern Europe and a large negative EFI indicative of low temperatures over western Europe.
...
Overview
Community Forums
Content Tools